Antenna pattern selection for optimized communications and avoidance of people

ABSTRACT

An antenna selection technique is used in an RF communincation system in which user modules (UM) communicate with at least one node. The UM&#39;s and nodes each have multiple antennae. The combination of each UM and node antenna is evaluated at the UM. Based on at least signal quality, the UM selects its antenna and the best node antenna for use. An alternate antenna is selected if a person is determined to be present in a predetermined area adjacent a UM corresponding to a predetermined RF power level.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 07/601,476 filedOct. 19, 1950, now U.S. Pat. No. 5,117,236 issued May 26, 1992.

BACKGROUND OF THE INVENTION

This invention generally addresses a communications system in which aplurality of spatially separated devices utilize RF communications andmore specifically addresses a method for selecting the best antennapattern from among several choices of antenna patterns. This inventionis especially suited for, but not limited to, an environment in whichmultipath signals and fading problems are significant such as in an RFcommunication system located inside a building. It also addressesantenna selection techniques which take the presence of people intoaccount.

It is generally known that directive antenna patterns can be utilized toenhance RF communications between remote RF transceiver. It is alsogenerally known that various means exist for controlling an antennaradiation pattern such as by rotating a highly directional antenna,controlling the phasing of different antenna elements to electronicallysteer the primary beam or radiation pattern, and the selection ofdifferent directional antennas targeted at different locations.

Methods for selecting an optimal antenna pattern vary greatly dependingupon the environment. In microwave line of sight communicationapplications, the antenna pattern selection is simple: just orienthighly directional antennas pointing at each other. Physically separatedantennas may be utilized by an RF transceiver to enhance communicationsthat are not line of sight. In such diversity applications each antennamay be monitored with the antenna having the optimal signal beingselected for use or all of the antennas may be combined utilizing theproper phasing to generate an enhanced single signal.

A number of factors make the problem of antenna pattern selectiondifficult. The reception of multipath signals, i.e. receiving the samesignal at different times with different signal strengths from differentgeographic locations, greatly complicates antenna selection. Theconstant fading of signals also adds to the problem. These factors arepresent inside a building in which RF transceivers communicate using the1-100 GHz(gigahertz) frequency range. The relatively close distancesbetween the antennae and reflectors, such as walls, floors, ceilings andother metal objects large relative to the wavelength, result in strongmultipath signals. Continuous fading results from environmental changessuch as the movement of people or objects. It is generally desirable tominimize a person's exposure to RF radiation. These exists a need for anantenna pattern selection method which optimizes communications in suchan environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an RF communication system employing anembodiment of the present invention.

FIG. 2 is a block diagram which shows an exemplary embodiment of an RFtransceiver with antenna selection in accord with the present invention.

FIG. 3 is a table illustrating different antenna performancemeasurements made in accordance with an embodiment of the presentinvention.

FIG. 4 is a flow diagram illustrating an embodiment of a method inaccordance with the present invention for generating the initialperformance measurements used in the table shown in FIG. 3.

FIG. 5 is a flow diagram in accordance with an embodiment of the presentinvention for selecting the best performing antenna at a node.

FIG. 6 is a flow diagram in accordance with an embodiment of the presentinvention illustrating a method for continuously updating and selectingthe best antenna for use at a user module.

FIG. 7 is a flow diagram in accordance with an embodiment of the presentinvention illustrating a method for continuously evaluating andselecting the best antenna for use at a node.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows an illustrative RF communications system having nodes N1and N2, and user modules UM1-UM5. The nodes and user modules eachinclude an RF transceiver enabling each user module (or remote device)to communicate with the nodes. The outside wall of one floor of abuilding is represented by dashed line 10. Interior walls 12 divide thespace into different areas. In the illustrated example, interior walls12 do not pass RF energy and in practice may constitute moveable metalwalls in an office environment.

Node N1 communicates with user modules UM1-UM3. Node N2 communicates theuser modules UM3-UM5. Thus, user module UM3 represents a common cellcapable of communicating with either node. Node N1 can also communicatedirectly with Node N2 by wire communication channel 14. Thus, each ofthe user modules can communicate with any of the other user modules inthis system. It should be noted that a user module such as UM1 may nothave a line of sight path of any node and thus must utilize acommunications path including at least one reflection. It will beapparent to those skilled in the art that UM's with a line of sightcommunication path to a node will also receive multiple reflectedsignals.

Module UM3 can communicate with node N1 by direct path 11 or path 13which includes one reflection off of wall 10. Beamwidths 11A and 13Aextend from module UM3 about paths 11 and 13, respectively, andrepresent areas in which the power of signals transmitted from UM3 usingthese paths are at or above a predetermined magnitude. It is desiredthat people avoid prolonged exposure to radiation at such magnitudes.Assume that the person shown in FIG. 1 begins to walk from position 15Ato position 15B, and that UM3 is transmitting over path 11. UM3 willswitch to path 13 shortly after the person enters area 11A and willcontinue to use that path as the person approaches area 13A. Shortlyafter the person enters area 13A UM3 will switch back to using path 11and will continue to use path 11 until a person enters area 11A or thepropagation deteriorates such that another path provides a bettercommunications path. The means used by the user module for avoidingprolonged radiation on paths where people are in the predetermined areaswill be explained below.

FIG. 2 illustrates an exemplary embodiment of an RF transceiver 16, anantenna selector 18 and a plurality of selectable directive antennasA1-A6 which maybe used as part of either a node or user module. In thisillustrative embodiment six unidirectional antennae with 60 degree beamwidths are located in a generally horizontal plane to give 360 degreepattern coverage. A data input/output channel 20 may be coupled to oneor more data devices. In the case of a user module, channel 20 could becoupled to a personal computer, an Ethernet port, or a digitized voicesource. It utilized as a node, the data input/output channel 20 mayconsist of a wireline data communications link 14 with other nodes andmay also be coupled to other data devices. The transceiver 16 contains aconventional receiver for receiving RF signals including appropriatedemodulation and decision making circuitry for decoding received signalsinto corresponding data. The transceiver also contains an RF transmitterwith suitable modulation and encoding circuitry to encode data to betransmitted over the RF carrier. The RF signals transmitted and receivedby receiver 16 are coupled to antenna selector 18 by cable or waveguide22.

The antenna selector 18 if capable of selecting any one of the sixantennas A1-A6 for use by transceiver 16. In order to rapidly select oneof the available antennas, electronic switching if preferably utilizedto select the desired antenna. Of course, conventional mechanicalswitching can be utilized if suitable for the particular application.The antenna selector contains a microprocessor and associated supportcircuitry for determining which antenna should be utilized as will beexplained in detail below. At microwave frequencies, the antennae mayconstitute horn antennae or other directive antennae and are preferablyarranged to provide complete 360 degree coverage in a horizontal planewith appropriate vertical beam widths to provide latitude for thereception of signals from virtually any location relative to the node oruser module. It will be apparent to those skilled in the art that theantenna selector 18 may be physically housed within transceiver 16 ifdesired.

In the illustrated embodiment of the present invention, communicationsbetween the nodes and user modules is accomplished using a time divisionmultiple access system in which packets of data are transmitted. Thenodes send packets containing an address and other related overheadinformation along with data destined for a user module which willrecognize this information by means of its unique address. Similarly,the user modules transmit messages to a node addressed for the nodeitself or another user module. Part of the information transmitted byeach node is the periodic transmission of reference packets which arereceived by the user modules. The bit error rate or other merit factorassociated with the reception of the reference packets along with thesignal strength is utilized in the antenna selection process which willbe described below.

In FIG. 3 Table 24 consists of a matrix of numerical values whichreflect a ranking of the antenna patterns, i.e. different antenna inthis embodiment. A separate value is calculated for each of thecombinations of antennas for a user module and a node, i.e. user moduleantennas 1i-6i and node antennas 1j-6j. In the illustrative embodiment,each user module maintains such a matrix for each node with which it cancommunicate. In the system as shown in FIG. 1, UM3 would maintain aseparate matrix for N1 and N2; the other UM's would maintain a singlematrix for the respective nodes.

Each user module generates a Table for each node with which it cancommunicates upon being put into service in such a system. In thissystem nodes and user modules utilize half duplex communications bysending information to each other. User modules preferably generate thevalues for the matrix based upon data received from each node. The nodetransmits the reference packets of data periodically using each of itsantennas 1j-6j and the user module receives the transmitted signals byperiodically selecting each of its antennas 1i-6i. Thus, after 36 suchcommunications Table 24 will have values for each cell. In a relativelyhigh speed communications system, such as utilizing packet transmissiontechniques, transmitting and receiving the required reference signals tocomplete the Table can be accomplished in a relatively short time.

The calculation of the value for each cell in Table 24 is based onsignal Quality (Q) and signal Strength (S) of the reference signalreceived by a user module antenna from a node antenna. Each receivedreference signal has a new rank (R) calculated as follows:

    R=(q*Q)+(s*S)                                              (1)

where q and s represent numerical weighting factors allowing the signalquality to be weighted differently than the signal strength. Theselection of each of these weighting factors will be somewhat dependentupon the communications system and the anticipated environment. In apreferred embodiment of the present invention, the signal quality has asubstantially greater importance than the signal strength and thus q>>s,i.e. q>10s. A conventional RF signal level sensing measurement may beutilized for signal strength. The signal quality may be measured bydetermining how many transmitted symbols exceed a predetermined receiverdemodulation window or may be based upon other known signal quality typemeasurements such as bit error rate.

The historical rank (HR) of the signal for each cell in the matrix isthe value stored in Table 24 and may be determined as follows:

    HR=(k*HR)+((1-k)*R)                                        (2)

Where k is a weighting factor which weights the historical rating HRrelative to a newly calculated new rating R, where 1>K>0. In thepreferred embodiment the historical rank is weighted substantiallyhigher than the new rank to prevent rapid changes in the cell value,i.e. k>0.5 such as K=0.9. This places more emphasis on the past historythan on the current calculation. This does not introduce an excessivedelay in selecting a different antenna when the table HR values areupdated frequently, such as every 24 milliseconds. As will be describedin more detail below, at least portions of this Table are beingcontinually updated to take into account a changing environment or otherfactors.

After each user module completes a Table 24 for each of the nodes withwhich it can communicate, the user module makes a determination of thebest node antenna. This determination is transmitted from the usermodule to each respective node thereby informing the node which of itsantennas to use when communicating with the user module. The user moduleantenna to be utilized for each node is selected at the user modulebased upon the Table. Since the Table at the user module is based uponsignals received from a node, it will be apparent to those skilled inthe art that this system, relies upon the principle of reciprocity inmaking the node antenna selection, i.e. it is assumed that the bestantenna for transmitting from the node to the UM is also the bestantenna for receiving signals from the user module. The antennaselection method according to the present invention allows additionaluser modules to be installed subsequent to initial system configurationwith automatic reconfiguration and selection of the best antennachoices.

FIG. 4 is a flow diagram illustrating the initial generation of valuesfor Table 24. Beginning at the START 26, variables n and i are set to 1in steps 28 and 30. The variable n represents the number of times theentire Tale has been calculated and in represents each user moduleantenna. In step 32 the reception of reference packets used for qualityand signal strength determination is enabled on local antenna i. In step34 parameter j is initialized to 1, j represents each node antennae. Instep 36 the user module constructing the subject Table enables receptionof a reference packet transmitted from node antenna j. Step 38represents a time delay allowed for the user module to receive thereference packet from the node. In step 40 a decision is made as towhether a new reference packet has been received. If YES, the new rank Rof the received reference packet is calculated in step 42. If NO, thenew rank is set equal to WORST which represents the worst possible newranking assignable to a call. Such a value is assigned to represent anunusable antenna combination since the reference packet was not receivedat all. The historical rank for the particular user module antenna andnode antenna combination is calculated at step 46. The historical ratingHR to each of the cells is stored in memory and is used for selectingthe user module and node antenna to be utilized as will be describedbelow.

In step 48, variable j is incremented by 1 thereby selecting the nextnode antenna to be utilized. A decision is made by step 50 to determineif the value of j exceeds the actual number of node antennas. A YESdetermination indicates it is within the maximum number of node antennasand steps 36-48 are repeated utilizing the same local antenna i but newnode antenna j. A NO determination by step 50 indicates that the UM hashad the opportunity to receive a referenced packet transmitted from eachof the node antennae, using the same local UM antenna and the usermodule antenna i is incremented by 1 in step 52. Decision step 54determines if the value i is within the maximum number of user moduleantennas. If YES, Steps 32-52 are repeated in which the i user moduleantenna receives reference packets from each of the node antennas j. ANO determination by step 54 means that each of the node antennas hastransmitted to each of the user module antennas thereby completing asample for each of the cells in table 24. The variable n is thenincremented by 1 in step 56. To avoid making an antenna decision basedupon only one sample of each cell and to build a history of such cellvalues before making the initial antenna determination, decision step 58determines if a sufficient number of samples of each of the cell valuesin Table 24 has occurred. If n has not yet achieved the required numberof samples, a YES decision causes steps 30-65 to be reexecuted therebygenerating another series of cell updates for the entire Table. A NOdetermination by step 58 represents that the predetermined number ofTable samples has been reached. This series of steps terminates asindicated by transfer to "A" 60. The parameter n will vary dependingupon the system configuration and the relative importance placed uponthe historical significance of the values of each cell in Table 24. Inthe illustrative embodiment of the present invention, n is desirablygreater than 10 and is preferably greater than 50 due to the emphasis onhistorical weighting.

FIG. 5 begins at entry point A 60 where variables j and i are eachinitialized to 1 representing node antenna 1j, UM antenna 1i at steps 62and 64. Step 66 in combination with steps 68 and 70 generate a valueequal to the sum of the values in column 1j. This column summationrepresents a composite value of the overall performance of each nodeantenna. Determination step 70 ceases looping back to step 66 when allof the values associated with each of the UM antennas has been summedfor one node antenna. Step 72 selects the next node antenna to have acolumn summation of HR values. Decision step 74 causes the precedingprocess to continue thereby summing each of the columns representingnode antenna values until all of the node antennas have a correspondingcomposite summation. A NO determination by decision step 74 indicatesthat all node antennas have summations that have been calculated. Instep 76, the node antenna with the composite summation j of the BEST sumidentifies the node antenna to be utilized for communication with thecorresponding user module. Step 77 ranks the UM antennae from best toworst based on the column in Table 24 associated with the registered orused node antenna. In step 78 the user module transmits the j nodeantenna selected to the node by a packet from the user module to thenode. Thus, the node now knows which of its antennas to assign whencommunicating with this particular user module. The steps end at point"B" 80.

These steps are carrier out at each user module for each node with whichit can communicate. Thus, a Table 24 will be calculated for each nodethat can be "seen" by a user module. Although each node does notmaintain a Table 24, it maintains in memory the antenna assigned to itby each user module for communications.

FIG. 6 is a flow diagram of an exemplary method in accordance with thepresent invention for determining and continuously, reevaluating thebest user module antenna. Before beginning these steps at point "B" 80,values for each cell in Table 24 will have been calculated and a nodeantenna selected. Parameters n, j, and i are initialed to 1 by steps 82and 84. Parameters i and j refer to user module antennas and nodeantennas, respectively. Parameter n will be explained below.

The reception of reference packets from node antenna j on local antennai is enabled at step 86. A time delay is introduced by step 88 toprovide time for reception of the reference packet. Decision step 90determines if a new reference packet was received. If NO, then the newrank R for the user module and node antenna combination is set equal toWORST, i.e. a very low rating value. Upon a YES decision by step 90 anew ranking is calculated by step 98. In step 100 the historical rank HRfor the subject antenna combination is updated to reflect the latest newranking.

Decision step 101 determines if all node antennae j have been sampled.If YES than step 103 increments j and steps 86-100 repeat for the newnode antenna. If NO by step 101, then decision step 102 determines ifany user module antennas remain to be evaluated in a cycle in which eachof the antennas are evaluated. A YES decision indicating more antennasare to be evaluated, causes step 104 to increment the user moduleantenna parameter i and a subsequent reevaluation for that antenna bysteps 86-100. A NO decision by step 102 indicates that all antennas havebeen reevaluated in a given cycle and the user module antennas areranked from best to worst for the values in the column of Table 24corresponding to the selected node antenna by step 106. The previousrankings for the user module antennae are maintained in memory. Decisionstep 108 determines if the latest ranking represents a change in orderfor the best rated user module antenna. If YES, the local antenna ischanged to the current best rated antenna by step 110. Following a NOdecision by step 108 or following action by step 110, decision step 112determines if the parameter n equals a predetermined value. Thispredetermined value is selected such that the node antenna will bereevaluated less frequently than the evaluation of the user moduleantennas. For example, if n=50, the node antennas would be reevaluatedonly after the user module antennas have been reevaluated 50 times. Ifthe value of n has not yet reached this predetermined evaluation value,i.e. a NO decision by step 112, parameter n is incremented by step 114and another cycle of user module antenna evaluations occur by steps86-110. A YES decision by step 112 causes the node antenna to bereevaluated by going to point "C" 116.

Subjecting people to prolonged radiation from the user module is avoidedby the continuous reevaluation process used in selecting the active usermodule antenna. Referring to FIG. 1, as a person enters area 11A whichcorresponds to the active antenna UM3, the user module will bereevaluating its antennae. Because a person entering this limiteddistance zone, such as a maximum of 1 or 2 meters from UM3, willsubstantially alter and likely degrade the propagation of signalsbetween UM3 and N1, the method according to FIG. 6 will cause anotherantenna at UM3 to be selected. When used in a packet signalling systemhaving very short packet lengths relative to the normal speed at which aperson moves this method will cause another antenna to be selectedwithin a few seconds thereby minimizing radiation exposure.

FIG. 7 is a flow diagram of an illustrative embodiment of steps inaccordance with the present invention by which the selected node antennais continuously reevaluated. Beginning at "C" 116, parameters i and jare initialized to 1 by steps 118 and 120. Step 122 calculates a longterm historical rating (LTHR) which is calculated in a similar manner tothe historical rating (HR) previously defined. In this calculation theweighting factor K may be selected to be different than the weightingfactor k for HR. This calculation step creates another table similar toTable 24 having the same format as Table 24 but representing an evenlonger term average of the values in Table 24. This table is utilized toprovide an even greater historical weighting to the evaluation of thenode antenna to be utilized. It should be remembered that Table 24 willhave been created and updated a number of times before the long termhistorical rating calculation in step 122 is made. Steps 124, 126, 128,and 130 combine with steps 120 and 122 to form a calculation nest bywhich each of the possible user module antennas and node antennas arereevaluated for the long term historical rating table. A YESdetermination by step 128 represents that each of these calculations hasbeen made. In step 132 a decision is made on whether the node antennashould be reselected. The decision criteria to cause a node antennareselection (YES), requires that the historical rating for the selecteduser module and node antennae be less than a short term (ST) thresholdand that the long term historical rating for a selected antennacombination be less than a long term (LT) threshold. It should be notedthat both the HR and LTHR requirements must be met. In the reference toLTHR [II, J] the II refers to the best long term value for a UM antennain the registered J node antenna column in the long term table. It willbe appreciated that for a given node antenna, the best UM antenna i inthe HR table may be different from the UM antenna II in the LTHR table.Different thresholds for each requirement can be selected to take intoconsideration the specific system configuration and environment. A YESdetermination by step 132 causes a return to point A60 and reselectionof a node antenna. A NO determination, causes a return to point "B" 80resulting in the continued reevaluation of user module antennas.

Subjecting people to prolonged radiation from the node is avoided by thecontinuous reevaluation process used in selecting the active nodeantenna. In the preferred embodiment the node has the same typedirectional antennae and effective radiated power as the user modules.Thus areas similar to those shown for UM3 in FIG. 1 exist relative toeach node antennae. Because a person entering the limited distance zoneadjacent the node will substantially alter and likely degrade thepropagation of signals between N1 and a user module, the methodaccording to FIG. 7 will cause another antenna at N1 to be selected.When used in a packet signalling system having very short packet lengthsrelative to the normal speed at which a person moves this method willcause another antenna to be selected within a few seconds therebyminimizing radiation exposure. Although the antenna reevaluation methodaccording to FIG. 7 will be shower than that for a user module, it willbe fast enough to prevent any prolonged radiation of a person within anactive area. Also, since the nodes are desirably placed at a centrallocation relative to the users and at a high location in a room orbuilding such as on the ceiling or on a support preferably at least 7feet above the floor, it is likely that people would normally occupy thedefined radiation areas.

It is believed to be apparent to those skilled in the art that theillustrative method relating to antenna pattern selection can beadvantageously employed as part of an overall operating system utilizedto control other parameters and communications in an RF communicationsystem. This method or selected parts of this method may be integratedinto a central control program and may be carried out as backgroundoperations as time permits relative to other uninterruptable or prioritytasks. Once basic communication is established between a user module andnode, the continuing reevaluation of the proper antennas to be utilizedmay not be critical depending upon the operating environment.

In the illustrative embodiment, each user module contains a table 24 ofvalues and a corresponding long term table of values for each node withwhich it can communicate. In the illustrative half-duplex communicationssystems shown in FIG. 1 it is believed advantageous to have the usermodules make selection determinations since such determinations can becarried out in parallel based upon a single transmission from a node.This method also facilitates the joining of a new user module into anexisting system since the complexity relating to antenna selection isdistributed among the user modules and not concentrated at the nodes.

One of the advantages of this invention is its ability to select themost appropriate antennae for use without requiring calibration of theRF transceivers. Selection of the antenna to be used is based torelative comparisons.

A further advantage of this invention is its ability to minimize aperson's exposure to RF radiation. In the illustrative embodiment of theinvention the disruption of the propagation of signals between a UM anda node is used as the means for limiting to radiation within a definedarea. Other means for limiting radiation exposure also be utilized. Alow frequency amplitude modulation detector that is electrically at ornear the transmitter as it feeds the antenna could be used to detect thedoppler shift between the transmitted signal and the echo from a nearbymoving object (person). Such a detection would be used to cause theselection of another antenna. Alternatively, a detection system could beemployed that would be independent of the transmitted signal. Anultrasonic detector or an infrared (heat) detector could be used tosense the movement or proximity of a person. Preferably such anindependent detector(s) would have a directional capability consistentwith the directional characteristics of the RF antennae so that antennaswitching decisions could be easily made.

Although an embodiment of the present invention has been shown andillustrated in the drawings, the scope of the invention is defined bythe claims which follow.

We claim:
 1. A radio frequency (RF) remote (RM) capable of RFcommunication with a communications system comprising:means forselecting an RM antenna pattern from a plurality of directional antennapatterns that cover different geographic areas relative to the RM; meansfor periodically generating a signal quality ranking for a plurality ofremote device antenna patterns for said RM based on signals communicatedbetween the RM and the communications system; said selecting meansselecting the RM antenna pattern having the best quality rank forcommunications between the RM and the communications system; meanscoupled to said selecting means for limiting a person's exposure to RFradiation from said RM when the person is within a predetermined areaadjacent said RM.
 2. The remote module according to claim 1 wherein saidlimiting means limits a person's exposure to RF radiation from said RMby sensing the degrading of signal quality associated with the selectedantenna pattern due to a person entering said predetermined area andcauses said selecting means to select a different antenna pattern. 3.The remote module according to claim 1 wherein said generating meansincludes means by evaluating the signal quality ranking of at leastcertain time division multiplexed packets that are periodically receivedby the RM.
 4. In a radio frequency (RF) communications system having aremote module (RM) capable of RF communications, a method of limiting aperson's exposure of RF energy transmitted by the RM comprising thesteps of:selecting an RM antenna pattern from a plurality of directionalantenna patterns that cover different geographic areas relative to theRM; periodically generating a signal quality ranking for a plurality ofremote device antenna patterns for said RM based on signals communicatedbetween the RM and the communications system; said selecting stepselecting the RM antenna pattern having the best quality rank forcommunications between the RM and the communications system; limiting aperson's exposure to RF radiation from said RM when the person is withina predetermined area adjacent said RM.
 5. The method according to claim4 wherein said limiting step limits a person's exposure to RF radiationfrom said RM by causing said selecting means to select a differentantenna pattern when a pattern in use has signal quality degradation dueto a person entering said predetermined area.
 6. The method according toclaim 4 wherein said generating step includes evaluating the signalquality ranking of at least certain time division multiplexed packetsthat are periodically received by the RM.